Method of producing metals and alloys poor in carbon and silicon



July 19, 1938- G. SAMUELSON ET AL 2,124,262

METHOD OF PRODUCING METALS AND ALLOYS POOR IN CARBON AND SILICON Filed Sept. '7, 1937 Patented July 19,1938

um'rso STATES PATENT .orrlcs METHOD OF PRODUCING METALS AND AL- LOYS POOR IN CARBON AND SILICON Frans Gustaf Samuelson, Osslan Henrik Jonson, and Klas Jonas Henrik Engdahl, Wargon,

Sweden, asslgnors to Wargiins Aktiebolag, .Wargon, Sweden, a corporation of Sweden Application September "I, 1937, Serial No. 162,754 In Sweden September 9, 1936 8 Ciaima 10 percentage of carbon, the introduction into the process of larger amounts of carbon by the raw materials used may be avoided. Moreover, in order to obtain a final product having a low percentage of silicon, the ore or oxide to be reduced ll must be used in a comparatively great excess with relation to the amount of silicon, in which case a great deal of the valuable alloying metal of the ore will be absorbed by the slag and be lost or a separate reduction process will be required in order to be recovered.

With a view to avoiding an increase of the carbon contents of the produced metal or alloy by the electrodes of the electric furnace in which the raw materials are melted, it ha'sialso been proposed to form electrodes from a mixture of the ore and the reducing agent used, preferably carbon, and melt themdown in an electric furnace. Suchv electrodes, however, are bad electric conductors so that for the purpose of applying the current, they must be provided with metallic cores or coatings'of considerable cross section. Due to the low conductivity of the electrode mass, the melting operation is still rendered diflicuit and the reducing process imperfect. If silicon or a silicon metal is used as a reducing agent,

the metal reduced from the ore will alloy itself.

to a large extent with silicon which cannot be removed afterwards without an expensive refining process and, if required, a remelting process 40 aswell. c

The present invention relates to a method of producing metals andalloys from oxides or oxide ores with the use of silicon or a silicon metal as a reducing agent, .by which process it will be possible, in a single operation and without the need of any special refining treatment, to obtain both a low content of carbon and a low content of silicon in the metal or alloy produced. According to the invention the oxide'or'ore to be reduced and the silicon orsilicon metal used as a reducing'agent, are intimately mixed together for the manufacture of electrodes by a method according to which said material at or subsequent to their forming to electrodes are treated by heat-- them to react, with the resulting ing to cause (on. 15-10) formation of a sinter in which the reduced metal -is distributed in the form of fine particles, giving the sintered electrode a high electric conductivity. Anelectrode consisting of such a sinter containing a metal melts very easily and uniformly in an electric furnace when fed down into a molten slag bath contained in the furnace, while applying an electric current through the electrode. In this melting process the fine metallic particles contained in the sintered electrode flow together, while being at the same time sub- Jected to a refining process, whereupon the molten metal collects so as to form a metal bath below the slag bath. 7

The invention will hereinafter be more fully described as applied to the continuous production of term-chromium from chromium ore with the use of ferro-silicon of. a high percentage of silicon as a reducing agent, reference being had to the accompanying drawing which illustrates, in a-substantially' diagrammatic way, the apparatus to be used in carrying outthe method according to this invention.

The chromium ore and the ferro-silicon are crushed and ground separately into a powdered state by means of appropriate apparatus, and

are then intimately mixed together, preferably,

with some excess of the ore over the quantity theoretically calculated to match the amount of reducing agent.

The mixture is then charged into a preheater I where it is preheated as unis. formly as possible, while stirring it, to a temperature slightly below that at which the silicon commences to react with the chromium ore, as for instance, to about 1000 C. Thepreheater which may, preferably, be made from some fireproof metahmay beheated by gas or oil or elec-' trically, as for instance, by'induction by means of high frequency electric current. The preheated mlxtureof the raw materials is then successlvely fed down into a vertical sintering tube 2 of thin sheet iron forming a housing forthe 'sintered mass and the finished electrode. The tube is extended by putting lengthening pieces on its upper end, in accordance with the melting of the finished electrode, as hereinaftendesc'ribed. At a distance below its upper end the sintering tube passes through a heating device which may comprise either a casing 3 annularly surrounding the tube which is proVided with oil or gas burning means, or an electric induction device for high frequency current, by means of which the portion of the tube situated within the heating device may be heated to the temperature required, as for instance, 1200 or 1250 0.,to effect V a reaction in the material fed down and the sintering thereof, inasmuch as the material here collects on the already sintered mass and is heated by its contact therewith as well as by an external supply of heat. By the reaction the chromium ore is reduced with the resulting production of ferro-chromium containing silicon and a slag consisting, substantially, of silicates which presents such a high viscosity as to cause the reduced metal to remain in a state of fine particles uniformly distributed in the sintered mass, said metal particles acting to give the sinter a very good electric conductivity. In the sintering process the mass of raw materials shrinks to less than half of its original volume. resulting in an increase of its specific gravity from about 1.8 to about 4. The reaction is of an exothermic nature and the heat evolved effects a considerable increase of temperature within the mass. Itis of importance that this increase of temperature does not continue until the slag becomes fluid, or melts, as in such case the reduced metal particles would flow together to form larger drops, whereby the electric conductivity of the sinter would be practically lost, thereby rendering the sinter useless as an electrode. The maximum temperature as attained during the reaction may be controlled by controlling the preheating operation and the external supply of heat to the sintering zone. After the process has started, the external supply of heat to the sintering zone may be essentially reduced, or even entirely dispensed with. The temperature may also be controlled by changing the composition of the mixture. An increase of the quantity of ore or an addition of slag forming substances will act to reduce the maximum temperature obtainable in the sintering zone, whereas an increase of the maximum temperature may be obtained by substituting for part of the ferro-silicon, a more active reducing agent, such as aluminium-silicon or calcium-silicon. Below the sintering zone the electrode loses its heat by radiation, causing the sintered mass to solidify completely while obtaining a high grade of mechanical strength. The lower end of the electrode depends into an electric furnace 4 containing a molten slag bath 5. Above said furnace the electrode is supported by gripping jaws 6 which also act to clamp current supply conduits 1 to the electrode, said jaws being provided with an appropriate feeding device by means of which the electrode can be fed down according as the upper end thereof is reestablished in the sintering zone from the raw material added and the lower end is molten in the furnace 4. CW-

ing tothe high electric conductivity of the electrode the melting operation proceeds very uniformly so that the lower end of the electrode will present a practically plane end surface in contact with the slag bath of the furnace. In the melting operation, the reaction between the ore and the reducing agent is completed under J the influence of the high temperature; at the same time a refining of the reduced metal takes place, said metal collecting below the slag bath in the form of a bath 8 consisting of molten ferro-chromium of a low carbon content and a low silicon content.

The following is an example of the practical application of the invention. As raw material an intimate mixture of finely powdered chromium ore and finely powdered ferro-silicon of high percentage was used, the, proportion being 1000 kg. ore and 200 kg. ferro-silicon. The composition of the chromium ore used was as follows:

The composition of the silicon iron was as follows: I

Per cent 81.... 95 Fe 3.1 A1 1 in the sintering zone could be shown by treating the produced sinter with acids, as for instance. hydrochloric acid. In treating the non-sintered powder with hydrochloric acid, only 0.10% Cr were dissolved; in treating a pulverized sintered mass in the same way, 25.6% Cr in the form of term-chromium of a silicon content amounting to 14 or 15% were dissolved. This dissolvable quantity of Cr contained 85.5% of the total amount of chromium. In treating the pulverized sinter with hydrochloric acid, none of the oxides contained in the base mass, was dissolved in a perceptible degree, because they were, no doubt, combined as acid silicates. insoluble in'acids.

The chromium-iron of high silicon percentage included in the sinter contained 14.8% Si, 60.0% Cr and 0.25% C. In melting the sinter electrode in the above described way, a chromium-iron was produced containing 1.9% Si, 64.0% Cr and 0.14% C. The refined slag as obtained in the electric furnace was approximately of the following composition: 58.5% $102, 9.6% CraCa, 13.5% A120: and 18.6% MgO. v

It is to be noted that the invention is not limited to the above described production of a sinter electrode which is immediately melted down; the mixture of raw materials can also be used for the production of sinter bodies of any desired length which c'onsist of a base mass of silicates with finelydivided-metallic particles included therein and these sinter bodies can afterwards he used, ir-

the tube. The sintering operation may also be carried out with the charged tubes in a horizontal position; in which case the sinter produced will fill about half the cross section of the tube throughout its entire length. In using these I Per cent ClzOa 52.5 FeO 13.2 SiOn 5.5 MgO 15.5 A1201 11.2 Glowing loss 1.6

blocks as electrodes with a view to eilecting their melting down, they may be joined by means of sheet metal shells in well known way.

The production of ferro-alloys of manganese, tungsten, vanadium or molybdenum is carried out in substantially the same way as above described in connection with the production of ierro-chromium. The method according to the invention may also be used in producing iron or steel alloyed with limited amounts of one or more of the above said metals without the risk of increasing the carbon content of the iron or steel. In this case the sintered electrode produced according to the above described method with its content of an iron alloy, of high silicon percentage, of one or more of the above said alloying metals, is used as an electrode in an electric furnace containing a molten bath of the iron or steel to be alloyed and is thus caused to melt, the alloying metal or metals being absorbed by the iron or steel bath, whereas the slag collects above the metallic bath to aid in the refining of the alloying metal in the melting process.

What we claim is:-

1. A method of producing metals and alloys poor in carbon and silicon, which comprises reacting upon a finely divided material containing an oxide of the metal to be produced by means of another finely divided material containing silicon, at such a low temperature that a sinter body having a good electric conductivity is termed, and

melting said body by using it as an electrode in an electric furnace.

2. A method of producing metals and alloys poor in carbon and silicon, which comprises forming a mixture of a-finely divided material containing an oxide of the metal to be produced and another material containing silicon, preheating said mixture, successively feeding the preheated mixture down into an upright mould, causing the constituents of the mixture to react upon each other in said mould so as to form an electrically conductive sinter body, immersing the lower end of said sinter body into a molten slag bath, and

successively melting the sinter body by electric energy supplied through it.

3. A method of manufacturing sintered bodiesadapted for use as electrodes in producing metals and alloys poor in carbon and silicon, which comprises forming a mixture of a finely divided material containing an oxide of the metal to be produced and a powdered silicon alloy, charging said mixture into a mould, heating the charge by external heat to cause the silicon alloy to react with the metal oxide so as to form asinter consisting chiefly of a silicate mass containing fine metal particles in uniform distribution, and lowering the temperature of the sinter to cause it to solidify.

' FRANS GUSTAF SAMUELSON.

OSSIAN HENRIK JONSON.

KIAS JONAS HENRIK ENGDAHL. 

